The present invention relates to the production of semiconductor wafers. The present invention has particular application for regulation of gas supply to a low pressure deposition process in the semiconductor wafer manufacturing industry.
The electronics industry continues to rely upon advances in semiconductor technology to realize higher-functioning devices in more compact areas. For many applications, realizing higher-functioning devices requires integrating a large number of electronic devices into a single silicon wafer. As the number of electronic devices per given area of the silicon wafer increases, the manufacturing process becomes more difficult.
A large variety of semiconductor devices have been manufactured having various applications in numerous disciplines. Such silicon-based semiconductor devices often include metal-oxide-semiconductor (MOS) transistors, such as p-channel MOS (PMOS), n-channel MOS (NMOS) and complimentary MOS (CMOS) transistors, bipolar transistors, BiCMOS transistors, etc.
Each of these semiconductor devices generally includes a semiconductor substrate on which a number of active devices are formed. The particular structure of a given active device can vary between device types. For example, in MOS transistors, an active device generally includes source and drain regions and a gate electrode which modulates current between the source and drain regions.
An important step in the manufacture of such devices is the formation of layers on the semiconductor wafer. Such layers are deposited using a number of techniques including physical vapor deposition (PVD), commonly known as xe2x80x9csputtering,xe2x80x9d and chemical vapor deposition (CVD) processes. CVD typically involves the formation of a non-volatile solid film on a substrate by the reaction of vapor phase chemicals that contain the required constituents. The reactant gases are introduced into a process chamber and are decomposed and reacted at a heated surface to form the thin film on the wafer. PVD primarily involves the deposition of conductive metals onto the wafer, accomplished by generating ions and directing them at a target in order to sputter target atoms, and then transporting the atoms to a wailer where they condense to form a film.
Another important step in the manufacture of such devices is etching. Etching is the erosion of selected portions of a surface in order to remove a specific material or produce a desired surface pattern. The process of etching is accomplished in a similar environment as CVD and PVD.
Typical configurations used in CVD, PVD, and etching processes include a process gas supply, regulated by a first control valve, a mass-flow controller downstream from the first control valve, a second control valve downstream from the mass-flow controller, and a process chamber downstream from the second control valve in which the CVD, PVD, or etching process occurs.
An important element in the operation of CVD, PVD, and etching processes is the delivery of process gas to the process chamber. A component that is used to control the rate of introduction of process gases into the process chamber is referenced to as a Mass-flow controller. Mass-flow controllers typically consist of a mass-flow meter, a controller, and a valve, and are located between a gas source and the process chamber in order to monitor and dispense gases at predetermined rates. Many mass-flow controllers perform well in the control of the delivery of the process gas during normal system operation. However, in many instances, mass-flow controllers are inadequate in controlling the supply of the process gas when first opening the valve to initiate the supply of process gas into the process chamber.
Due to the difficulty in controlling the supply process gas, pressure bursts occur in the process chamber when first opening the second control valve between the mass-flow controller and the process chamber. These pressure bursts may effect a wave of pressure across the process chamber, and may ultimately result in significant defects on and in the product wafer surface film. A reduction in these bursts is a positive step in the direction of eliminating defects.
The severity of the pressure control problem discussed above is lessened by the use of the method and apparatus described herein. According to one example embodiment, the present invention involves the use of an apparatus for controlling the pressure of supply fluid between a mass-flow controller and a process chamber, wherein the apparatus comprises a valve coupled to the fluid path between the mass-flow controller and the process chamber, and wherein the valve includes a control, responsive to a control input. The apparatus further comprises a second control for controlling the control input, thereby inhibiting pressure bursts downstream in the process chamber.
In another example embodiment, the present invention includes a process for controlling chamber pressure during the manufacture of a semiconductor chip, wherein the process takes place in a system including a mass-flow controller and a process chamber located downstream from the mass-flow controller, and wherein the process chamber is susceptible to significant pressure bursts upstream therefrom. The process includes coupling a pneumatically-operated valve to a first fluid path between the mass-flow controller and the process chamber. The pneumatically-operated valve includes a diaphragm, responsive to a second fluid pressure, that controls the operation of the valve. The process further includes coupling a metering valve to control the second fluid pressure. The metering valve is slowly adjusted, and the second fluid pressure to the diaphragm is altered, thereby inhibiting pressure bursts downstream to the chamber.
The above summary is not intended to characterize each embodiment of the present invention. Other aspects of the present invention will become apparent upon review of the figures and corresponding xe2x80x9cDetailed Descriptionxe2x80x9d.